Swimming pool guard alarm unit

ABSTRACT

A device for monitoring wave action on the surface of water in a swimming pool in a manner to sound an alarm when someone either accidentally falls into a swimming pool or uses the pool without authorization. A buoy floats on the surface of the swimming pool for detecting excessive wave action. At least one positionsensitive switch is attached to a pivotably mounted float within the buoy for detecting such wave action. A signal from the switch in the buoy is transmitted to a remote alarm unit either by a direct wire connection or by a low power radio transmitter located within the buoy.

Jahn

[ SWIMMING POOL GUARD ALARM UNIT [75] Inventor: Darrel S. Jahn, M untainView.

Calif. Y

[73] Assignee: Aquatic Systems, Inc., Sunnyvale,.

Calif.

[22] Filed: Sept. 27, 1971 [21] Appl. No.: 184,085

[51] Int. Cl. G08b 13/00 [58] Field of Search 340/261, 258 R, 421,340/244 B, 224; 200/612, 84 R, 230

[56] References Cited UNITED STATES PATENTS 2,816,973 12/1957 Beck et al340/244 B 3,636,544 111972 Codina 340/224 3,329,935 Wiggins 340/261 11]3,7?7S,803 1 Dec. 11, 1973 Primary Examiner.loh n W. Caldwell i Assista'm Examiners-Glen R. Swann, III AttorneyGerald P. Parsons et al.

[57]" ABSTRACT 7 or by a low power radio transmitter located within thebuoy.

7 11 Claims, 8 Drawing Figures PATENTEB DEC 1 I I975 3L718'.803 sum 3 BF4'' w INVENTOR,

BARREL .8. JAHN BY I WW .8

ATTORNEYS minimum 1 1 ms 3.778.803 sum w 4 INVENTOR. DARREL S. 'JAHNATTORNEYS 1 SWIMMING POOL GUARD ALARM UNIT BACKGROUND OF THE INVENTIONThis invention relates generally to the art of sensing wave motion onthe surface of a body of liquid, and more specifically relates to suchdevices designed for use on the surface of a swimming pool for detectinguse of the pool.

is often desirable to be able to monitor an unattended pool to detect anunauthorizedperson using the pool. There. are several commerciallyavailable units for monitoring the use of a swimming pool, but theseunits suffer from certain disadvantages that are overcome by themonitoring device of the present invention.

In one such commercially available device, a sensor is held a few inchesbelow the surface of the swimming pool water by anchoring an electricalcontrolcord to the pool bottom. The control wire is then connected to analarm unit in an adjoining house or other structure. A difficulty withthis type of device is that it has to be removed before the pool may beused for swimming. This device is battery operated and sounds an alarmcontinuously until shut off manually, thereby running down the batteriesif someone does not immediately hear the alarm. The device isineffective until the dead battery is discovered. Additionally, thistype of device may be disabled by an unauthorized person by firstcutting the wire between'the sensor in the pool and the alarm in theadjoining structure.

Another type of device that is commercially available is self-containedand floats on the surface of a pool. Gas

. under pressure is released when wave action reaches a threshold level.A horn on the device is then sounded.

The pressurized gas is contained in a removable cannister that may bereplaced after the unit has once sounded. The primary difficulty withthis type of pool monitoring unit is that once it sounds and uses allthe pressurized gas of a cannist er installed therein, the unit is nolonger effective. If the alarm is sounded while no one is within rangeof the pool to hear it, it will not be known that a new pressured gascannister need be in stalled. Furthermore, such a device may be easilydisabled and removed from the pool by someone desiring to use the poolwithout authorization.

Yet another type of pool monitoring unit utilizes a sound transducerinstalled along the bottom of a pool and is connected with a remotealarm unit by wires. The main difficulty with this type of monitoringdevice is that it may not always pick up surface noise such as thatcreated by a child or an animal falling into the pool. The soundtransducer is activated if a swimmer moves around but may not respond toa mere splash in the pool.

Therefore, it is an object of the present invention to provide aswimming pool monitoring device which can detect both a family pet orchild falling into apool as well as detecting unauthorized use of thepool.

It is another object of the present invention to provide a poolmonitoring device which looks like some other commonly used poolaccessory in order to disprovide a pool mo nitofing device which isdifficult to disable without sounding an alarm.

I It is still a further object of the present invention to provide apool monitoring device that does not quickly consume its self-containedsource of power to render the device inoperative without the knowledgeof those using the device.

SUM MARY'OF THE INVENTION These and additional objects are accomplishedby the pool monitoring device of the present invention which includes abuoy that floats on the surface of the pool and is designed to look likean ordinary pool chlorinator. A ring of flotation material supports acylindrical container mounted in an upright position. A float is mountedin the container and carries at least one positional sensitiveelectrical switch. When surface wave action from a person falling,jumping or diving into the pool disturbs the float, the electricalswitch is activated which sets off an alarm in a remote unit. The floatis preferably pivotably attached to the interior of the container. Whenthere is excessive wave action in the pool, the float is rotated aboutits pivot into a position that is different from the normal position.The entire container is made adjustable with respect to the ring offlotation material (and thus with respect to the pool water surface) inorder to adjust the sensitivity of the device so that normal wavesgenerated by the wind will not tilt the float enough to change the stateof the switch.

In order to also detect when the device is withdrawn from the swimmingpool by an unauthorized person, a second positional-sensitive switch iscarried by the pivotably mounted float. The second switch is in adifferent position on the float from the first switch. In a specificpreferred embodiment, the float is normally held slightly below ahorizontal position by the water level of the swimming poolwhen thecontainer is properly adjusted on the ring of flotation material. Thefirst switch is oriented to change its state when the float is caused torise by wave action. The second switch is oriented on the float tochange its state when the float falls to a substantially verticalposition. Having two switches makes it extremely difficult for anintruder to withdraw the buoy from the swimming pool without changingthe state of one of the switches which activates a remote alarm.

A change of state of either of the switches located in the bony istransmitted to a remote alarm unit either by wire or by the use of aradio frequency transmitter within the bouy. Use ofa radio frequencytransmitter rather than a wire connection has an advantage of providinggreater flexibility in remote positioning of the alarm unit. The alarmunit may even be moved to a neighbors house for monitoring of the poolwhen the pool owner is away for an extended period. In either of theradio transmitter or wire connection embodiments, the switches withinthe buoy are normally in an of state. When either of the switches isclosed (turned to its on" state), an audio alarm begins to sound. Thealarm continues to sound even though the buoy switch is only on for aninstant. A time delay circuit within the alarm unit allows the audioalarm to sound only for an adjusted predetermined period of time.

sertion in the buoy of FIG. 1;

In the radio transmitter embodiment, a small battery operatedtransmitter is installed within the cylindrical container of the buoy.The transmitter is operative only during the period of time that eitherone of the two position sensitive switches is closed. The frequency ofoperation of the transmitter is chosen to be within a band permitted forunlicensed low power transmitters by existing F.C.C. regulations. Aspart of the transmit- 'ter, the radio requency signal is modulated by aconstant frequency audio oscillator but just outside of the 17, ahdthusthe elevation of the'container 19 with re spect to the water surface 13,may be adjusted by rotating the container 19 w ith respect to the float17. A scale 23 formed onthesurface on the container 19 indicates itselevation with respect'to the float 17. An

' opening 25 is provided in thebottom of the container 19 for water topass into the container. Additionally, an

: opening 27 is provided on the side of the container 19 in order toopen the volume inside the container and normal audio frequency range.The remote alarm unit contains a receiver for receiving the radiofrequency; signal and demodulating it. A highly selective filter uni-tis made as part of the receiver so that the alarm is activated only whenbuoy transmitter modulating frequency is received. In making themodulating frequency something outside the audio range, the chances thatthe alarm of the receiver will be set off by voice operation of atransceiver on the same radio frequency as the buoy transmitter issubstantially eliminated.

above the water level to atomspheric air pressure. A flattened space,not shown, on the side of the container 19 extending'beneath the scale23 provides an air passage to the opening 27 from the region above thefloat 17. A disturbance on the surface 13 of the swimming pool'isreflected into the container 19 in the form of a surface disturbance ofthe water therein. It is the distur- Further objects and advantages ofthe present inven- 7 tion will become apparent from the descriptionwhich follows when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG; 1 is a side view of a buoycontaining a radio frequency transmitter according to one aspect of thepresent invention;

FIG. 2 is a partially cut away view of a container portion ofthe buoy ofFIG. 1;

FIG. 3 is a sectional view of the container of FIG. 2 taken acrosssection 3-3;

. FIG. 4 is a partial view of the broken away container of FIG. 2 underdifferent conditions;

FIG. 5 is a circuit diagram of radio transmitter for in- FIGS. 6A and 6Bshow a radio receiver and alarm circuit diagram for the remote alarmunit; and

' FIG. 7 shows a circuit diagram for an alarm unit that Y is connectedby wire to a buoy, according to another aspect of the present invention.7

,- I DESCRIPTION OF THE PREFERRED EMBODIMENTS buoy 11 floating on a FIG.1 shows a surface 13 of swimming pool water 15. The buoy 11 includes'twoprincipal components. A volume of flotation material 1 17 is formed inthe shape of a ring with a circular opening in its center for receivinga cylindrical container 19. These two components may be essentially thesame as corresponding components of existing floating swimming poolchlorinators which are designed and sold for floating on the surface ofswimming pools to dispense chlorine at a constant slow rate. The buoyll, of I course, does not serve a function of chlorinating a swimmingpool but its overall appearance as a pool I chlorinator conceals itstrue function to an intruder who may attempt to disable an obvious alarmunit before using the pool.

The float 17 is preferably made ofa light plastic foam material. Thecontainer 19 is in the shape of an elongated cylinder and isxpreferablymade of a thin watertight plastic material. A single thread extendingoutward from the inner surface of the center hold of the float ring 17,not shown, supports the container 19 somewhere along its externalsurface threads 21. The

elevation of the container 19 with respect to the float bance of thewater level within the container 19 that is detected by the 'buoy 11.When this disturbance is greater than a threshold amount, a radiotransmitter within the container 19 is operated to emit a radio fre- Vquency signal from a wire antenna 29 attached to the inner surface of acap 31. The cap 31 is affixed tothe container 19 in a water-tightmanner.

, A rigid plastic disc 33 forms a water-tight compartment flected withinthe container 19.

Referring to FIG. 2, an enlarged partially broken away view of thecylindrical container 19 is illustrated.

at the upper end of the container 19 for housing a transmitter and itsbattery in cavities 35 and 37, respectively. The cavities 35 and 37 areformed'by'heat and shock-absorbing plastic foam pieces 39 and 41.

Below the rigid disc 33 is the region of thecontainer 19 which receivesswimming pool water. A block of lightweight plastic material is formedinto the shape of a float 43. A rigid plastic rod 45 is attached to thefloat 43 and is pivotably mounted in rigid plastic blocks 47 and 49 ateither end of the rod 45. The blocks 47 and 49 are firmly attached tothe underside of thedisc 33.

Position sensitive switches 51 and 53 are, embedded within the float 43by cutting holes in the float, inserting the switches therein andthensealing the switches with a silicon rubber fluid which forms awater-tight seal. The pivotable position of the float 43 is controlledby the height of the liquid surface within the container 19. Theelectrical switches 51 and 53 thereby sense the level of the swimmingpool surface as re- The switches 51 and 53 are preferablyof the typewherein an elongated generally cylindrically shaped glass tube is filledwith a small amount of electrically conducting liquid such as mercury. Apair of conductors within each tube are normally spaced apart andinsulated until the switch is oriented in a position to cause themercury to flow and join the two electrodes in a complete electricalcircuit. In the position of the float 43 shown in FIG. 2, a pool ofmercury 54 restsat an end a within the glass tube of the switch 51.Since the pair of electrodes are at the end b of the switch 51, noelectrical connection is made and the switch is in an off" state. Aswave action on the swimming pool surface increases above some thresholdlevel, the level of the liquid surface 55 within the container 19 willraise the float 43 into a horizontal position or above, thus causing themercury pool 54 to flow toward the end b within the switch 51' and thusmade an electrical connection between its bare pair of electrodes. Theswitch 51 is then in its on state. The sensitivity of the switch 51' isadjusted by raising or lowering the container 19 The internal electrodes,of the switch 51 are connected by a flexible wire pair 57 to thetransmitter, in

a manner discussed hereinafter, to transmit an alarm signal to a remote.alarm unit. The switch 51 need be changed from its normal of state toits on" state only for an instant to cause a pulse of radio frequency tobe emitted by the antenna 29 and cause an alarm to be sounded in aremote location. Therefore, a single wave of a sufficient amplitude willoperate a remote alarm. i

I The second switch 53 is connected electrically in parallel with theswitch 51 and to the pair of conductors 57 so that the transmitter emitsa signal when either of the switches are caused to be thrown into theiron state. The switch 53 has a pool of mercury 59 at its end when thefloat 43 is in the position shown in FIG. 2.

No electrical connection is made in this position between a pair ofconductors within the switch 53. However if the buoy 11 is removed fromthe water by someone attempting to disable the device, the float 43falls to a position shown in FIG. 4. The switch 51 remains in its ofstate but theswitch 53 is oriented in FIG. 4 so that its mercury poolhas travelled to the end d of the switch, thus making contact betweenthe two electrodes of the switch 53. The pair of wires 57 are thenconnected together. The radio frequency transmitter thusemits a signalwhich sounds an alarm in a remote alarm unit. I v

The float 43 is shaped to have a point 61 extending from itsbottom sidefor contacting a side wall of the container 19 as shown in FIG. 4 whenthe buoy is withdrawn from the swimming pool water. The reason for theextension 61 is to hold the center of gravity of the float 43 at aposition that is to the left of the pivot rod 45 when the float isin theposition shown in FIG. 4.

When buoy 11 is put back into the water, therefore,

water rushing in through the opening 25 at the bottom of the container19 will not hold the float 43 in the position shown in FIG. 4 but ratherwill cause it to pivot clockwise with its position determined by theresulting level of the water within the container 19.

The swimming pool owner probably desires to remove the buoy 11 while thepool is being used with his authority or when being cleaned in order toprevent repetitive pulses from being emitted from the radio transmitter.Continued operation of the transmitter can run down itsbattery. In orderto prevent the float 43 from i falling to the position shown in FIG. 4,where the switch 53 will keep the transmitter on, a volume of deformableplastic (not shown) is provided for insertion through the opening 25.Such a volume of plastic is designed to hold the float 43 at less thanhorizontal to prevent operation of the switch 51. This technique doesnot avoid operation of the remote alarm since it is difficult to inserta plastic block without setting off at least one transmitter pulse.

A detailed circuit diagram of the radio frequency transmitter forinstallation in the container 19 is shown in FIG. 5. An electricalrepresentation of the switches emit a radio frequency signal from theantenna 29. A crystal 67 controls the frequency of oscillation of radiofrequency oscillator circuit which includes the transis tor 0,. Thetransmitter of FIG. 5 operatesin the 27 megacycle range so the crystal67 is chosen for a partic ular frequency in this range.

. the 27 megacycle range. The exact frequency of the oscillator 69 canbe varied by changing both of the capacitors C, and C from the valuesshown in FIG. 5 to some other specific value. C and C are kept atsubstantially the same value. 1

Te particular circuit diagram of FIG. 5 is a modified commerciallyavailable super-regenerative transceiver. The commercially availablevtransciver may be wired permanently to operate in the transmit mode andit voice circuitsare replaced by the single frequency oscillator circuit69. Of course, there is a wide variety of different types of miniaturelow power transmitters that may be utilized as part of the presentinvention.

A preferred receiver for receiving the signal transmitted by thetransmitter of FIG. Sat a location remote from the buoy is illustratedin the form of a detailed electronic circuit. diagram in FIG. 6A and 68.Such a receiver and alarm circuit can be mounted in a small box within ahome adjacent the pool in which the buoy is floating for monitoring itsuse while unattended. The radio frequency signal is received at thereceiver antenna 71 of FIG. 6A and an audio signal is demodulatedtherefrom by a receiver section enclosed by the dotted lines andindicated by the reference number 73. The audio signal being demodulatedfrom the radio frequency signal received is presented at terminals 75and 77. The receiver section 73 of the FIG. 6A circuit is again one thatis commercially available, as part of a superheterodyne transceivercircuit. The commercially available transceiver is modified to operatepermanently in its receiving mode, and additional components of thetransceiver dealing with other functions than merely demodulating aradio frequency signal to obtain an audio signal therefrom are not used.

A power supply circuit 79 is provided for developing v the requiredpositive DC voltage at a terminal 81 with respect to a neutral terminal83. Also, the power supply circuit 79.develops a negative direct currentvoltage at a terminal 85, with respect to the neutral terminal 83.Although the circuit of FIGS. 6A and 68 could be operated by batteries,it is felt preferable to use ordinary house'current. Since current isconsumed by the circuit of FIGS. 6A and 63 throughout the period thatthe pool 'is being monitored, the use of batteries and the inconvenienceof having to replace them at periodic intervals is avoided.

The demodulated audio signal at terminals and 77 is operated upon by anelectronic filter section of the circuit of FIG. 68 indicated at 87. Thefilter unit 87 includes the use of four operational amplifiers 89, 91,93, and 95, all connected in series. The filter unit 87 is a highlyselective filter which presents a voltage at its output terminal 97 onlywhen the input signal is very close to the center frequency to which thefilter unit 87 is tuned.

' The first three operational amplifiers 89, 91, and 93' of the filtersection 87 of the FIG. 6B circuit comprise the actual filter while thelast operational amplifier 95 serves to provide voltage amplification.To adjust the filter circuit 87, a modulated signal is transmitted'tothe receiver of the circuit of FIG. 6A. The potentiometers 99 and 101are then adjusted for a peak voltage output ,at theterminal 97. Thereceiver is then adjusted for its" mating buoytransmitter. The filter 97is narrowly received at the antenna 71 which has been modulatedby theaudio range frequency to which the filter section has been tuned. Whensuch a signal is received, the

voltage at the terminal 97 jumps to a maximum value.

However, the current available atthe output terminal 97 is notsufficient for driving a relay and time delay t ube. Therefore, acurrent driving circuit 103 is connected to the output of the filtercircuit 87 and includes a transistor which acts as a power amplifier. Anoutput terminal 105 of the current driving circuit 103 is connected witha signal circuit 107.

A relay coil 109 is connected between the output terminal 105 of thedriving circuit 103 and to the positive 'DC supply developed at powersupply output terminal 81 in series with a normally closed circuitbreaker 111.

t The circuit breaker 111 is part of a delay tube to be described below.The relay includes switches 113, 115, and 117 which are normally held inpositions shown in FIG. 6B absent a current being applied to the relaycoil 109 of sufficient magnitude to move the switches to their alternatepositions. I

When in the rest position shown in FIG. 6B the power supply circuit 79is connected with the filter circuit 87 through the relay switches. Therelay switch 113 normally connects the positive direct current voltagefrom the power supply 79 to the filter circuit 87.

The relay switch 117 normally connects thenegative. direct currentvoltage to the filter circuit. When a signal is received that movesthese relay switches to their second positions, however, both thepositive and negative direct current voltage are disconnected from thefilter circuit in order to prevent any spurious signals 'from beinggenerated At the same time, the relay switch 115 connects to ground theterminal of the relay coil 109 that is continually connected with thedriver output terminal 105. This keeps the relay coil 109 energized andeven though after the first instant there may no longer be a signal atthe terminal 105 that will drive the relay coil 109. This keeps therelay switches 113,

that is ihdependent of the length of this radio frequency pulse.

When the relay coil l09 is energized, the switches f 113 and 11 5connect-the positive direct current and ground, respectively, across anaudio horn 119. Connected parallel with the horn 119, and thus alsoacross the positive direct current source, is a heating element of tacommercially available delay tube, indicated by the resistance 121. Whenthe heating element 121 has been connected across the positive directcurrent source for a time sufficient to reach a predetermined level, thecircuit breaker 111- is thrown, which disconnects the entire circuitfrom the positive direct current output terminal 81. At this point, therelay coil 109 is also disenergized and the switches 113, 115 and 117are returned to their rest position shown in FIG. 6B. The sounding ofthe horn is. then discontinuedand the resistance element 121 of thedelay tub is disenergized. When the resistance element 121 coolssufficiently, the

-circuit breaker 111 automatically returns to complete the positivedirect current circuit to supply the remaining portion of the receiverand alarm circuit. Thereceiver is then ready to detect the next radiofrequency signal from the buoy.

The particular type of delaytube of which the resistance element 121 andthe circuit breaker 111 are a part is chosen for the length: of time thehorn 119 is desired to sound when a large wave on the surface of theswimming pool strikes the buoy. If a short time is required, acommercially available 6C5 delay tube may be used for about a S-secondhorn blast. If about a 30- second sounding of the horn is desired, a6C30 delay tube may be used. I

The transmitter andreceiver circuits of FIGS. Sand 6A and 68,respectively, have the advantage that several buoys may be employedv inseveral swimming pools and monitored by a single receiver/alarm unit.The audio oscillator 69 (FIG. 5) of each buoy is tuned to a uniquefrequency by having the capacitors C, and C, fixed at a unique value foreach buoy. The receiver circuit of FIG. 6B is then modified to include aplurality of filters 87 in parallel, one filter tuned to the audiooscillator frequency of each buoy.

'For reasons primarily of economy, some users may prefer a direct wireconnection between the positional sensitive switches of the buoy and analarm unit rather 7 than the radio frequency connection described above.

In such a case, of course, the transmitter and battery FIG. 1, and oneend ofa long wire is connected with the switches 51 and 53. The alarmunit installed in an adjoining structure is connected to the other endof the long wire and is greatly simplified from the receiver/a- Iarmunit of FIGS. 6A and 68. FIG. 7 shows a preferred circuit for the alarmunit which is connected by wire to the switches 51 and 53 of the buoy. Adouble-pole, double-throw relay is used having a coil 123 and switches125 and 127. The switches 125 and 127 are shown in FIG. '7 in their restposition when the relay coil 123 is not energized, and it-will be notedthat in this state no electrical connection is made by the relayswitches.

A circuit breaker 129 is part of the delay tube which also includes aheating element denoted by the resistance 131, similar to the signalcircuit 107 of FIG. 6B. A low direct current voitage source, preferablyfrom a battery, may be connected across terminals 133 and 135. A masteron-off switch 137 is connected to the oneeIectrical state when liquid isbelow a predeterpositive voltage source terminal 133. A battery maybemined level within the container and a second elecused in this casesince the circuit is operative only for trical state when liquid isabove said predetermined a short time after either of the buoy switches51 and 53 legel, a f; is momentarily closed. A horn 139 sounds an alarmmeans electricallyv connected with said switch for when one of theswitches of the buoy is instantaneously communicating its state to aremote location, closed. whereby waves on the surface of the liquidcause ,2 The principle of operation of the circuit of FIG. 7 is saidpivotably mounted float to change its angular 5 similar to that of thesignal circuit 107 of the more position relative to said container andsignals said i complicated receiver/alarm unit of FIGS. 6A and 6B. 10positional change to said remote location, and

When the on-off switch 137 is closed, the relay coil 123 a secondtwo-state position sensitive switch carried 1 i is connected across thevoltage terminals 133 and 135 a by said pivotably mounted float andoriented genwhen either of the switches 51 and 53 in the buoy are erallyto be in one of its states when liquid is near closed for an instant.When this occurs, the switches said predetermined level within saidcontainer and 125 and 127 of the relay are moved to the alternate poinanother of its states when the float is not sup sition from that shownin H6. 7. The switch 125 then ported against gravity within thecontainer. connects the relay coil 133 across the power input terj 2. Aswimming pool alarm unit, comprising: minals 133 and 135 to lock therelay after the switches a volume of material for floating on thesurface of the 51 and 53 both become open again. After the relay isswimming pool, said volume of material formed in so thrpwn, the horn 133sounds and the heating eler the shape ofa ring having a circular openingin its ment 131 of the delay tube is connected across the voltcenter, 1g age input terminals 133 and 135. a tubular container positioned withinthe opening of This circuit state occurs until the heating element saidring and threadedly engaged therewith in a 131 of the delay tube getshot enough to throw the cirmanner that the container may be moved up andcuit breaker 129 of the delay tube. When the circuit down relative tothe ring by twisting's'aid container breaker 129 is thrown, the inputvoltage across termiwith respect to thering, nals 133 and 135 isdisconnected from all of the circuit 3 said container including a waterinlet opening in the elements, including the relay coil 123, the horn139 v H vacinity of its bottom and an air opening in the and the heatingelement 131 of the delay tube. The vacinity of its top, thereby allowingwater to rise horn then stops blowing, the relay switches 125 and withinthe coritainer to a level porportiorial to the 127 return to their restposition shown in FIG. 7, and water surface level surrounding said ringof flotathe heating element 131 of the delay tube begins to tionmaterial, cool. When the heating element 131 is cooled suffiat least oneposition sensitive electrical switch within ciently, the circuit breaker129 returns to its position said container positioned to detect thewater level shown in FIG. 7 to connect all of the elements to the withinsaid container, and voltage input supply. The circuit is now ready foranmeans electrically connected with said switch for other pulse bymomentary closing of either. of the communicating its state to a remotelocation. switches 51 and 53. lt will be noted that the direct wire 3.Apparatus for monitoring surface waves on a body connected embodiment ofthe alarm system of the presof liquid, comprising: ent invention asshown in P16. 7 also has the advantage a piece of flotation material forsupporting the appa- W that the length of time that the horn 139 issounded is ratus on the liquid surface, li independent of the length oftime that one of the a float pivotably mounted with respect to saidflotaxii switches of the buoy is closed. The length of the horn tionmaterial in a manner to be supported against I blast may be set bychoice of the delay tube. gravity by the liquid surface, said floatincluding a The present invention has been described in its 'pre- 5block of plastic material with a pivot rod extending ferred specificembodiments and it will be understood through one end thereof forsupporting the float that the full scope of the invention is defined bythe apwith respect to said flotation material in a manner pended claims.v to be rotatable with respect thereto,

What is claimed is: at least one position sensitive electrical switchem- 1. Apparatus for monitoring surface waves on a body 7 bedded in saidpivotably mounted float in a manner of liquid, comprising 1 to have oneelectrical state when the liquid surface a piece of flotation materialfor supporting the appais calm and a second electrical state when aliquid ratus on the liquid surface, 7 surface wave of sufficientmagnitude strikes the floa container supported by said flotationmaterial in a -tation material, and

manner to be partially submersed below the liquid meanselectricallyconnected with said at least one surface, said container having anopening in the switch for communicating its state to a remote lovacinityof its bottom for liquid to pass therecation, whereby waves on thesurface of the liquid through into said container and an air opening incause said pivotably mounted float to change its the vacinity of itstop, thereby allowing liquid to 1 angular position relative to saidcontainer and sigrise within the container to a level proportional tonals said positional change to said remote location.

the height of the liquid surface surrounding said 4. An alarm systemaccording to claim 3 wherein the flotation material, single frequency ofthe transmitter audio oscillator is a float pivotably mounted withinsaid container, the outside of the normal voice frequency range range.

angular position of said float being controlled by 5. An alarm systemaccording to claim 3 wherein said the level of liquid within thecontainer, means for sounding an audio alarm includes a switch a firstposition sensitive electrical switch carried by means operable inresponse to a momentary signal outsaid pivotably mounted float in amanner to have put from said filter to connect an audio sounding deviceand a delay tube to a power source for a predetermined period, saiddelay tube being connected in a manner to disconnect said power sourcefrom the audio sounding device and the delay tube after a period ofsignal, and further wherein said receiver includes a fil-' ter circuittuned to the single frequency of the audio oscillator to enable saidindication means when the received signal includes the modulating singlefrequency.

7. Apparatus according to claim 3 wherein said means for communicatingthe state of said at least one switch to remote location includes:

a radio frequency transmitter carried by said flotation material andconnected with said at least one position sensitive switch in order totransmit a signal when said at least one switch isin its said secondstate, and I a radio frequency receiver located in a position remotefrom said flotation device and tuned to receive said radio frequencysignal, said receiver includes means for giving an indication uponreceipt of said signal.

8. Apparatus according to claim 4 wherein said indication means containsan alarm means for sounding an audio alarm for a predetermined timeafter first receiving the radio frequency signaL'whereby' a mere pulseof radio frequency energywill sound an alarmof said receiver for saidpredetermined time.

9. Apparatus according to claim 6 whereinsaid means for communicatingthestate of said at least one switch to a remote location includes:

a length of wire electrically connected with said switch and extendingfrom said flotation material to said remote location, and

a signaling device lo'cated at said remote location and connected withsaid switch by said length of wire,

said signaling device being operated when said at least one switch is inits second state.

10. Apparatus according to claim 9 wherein said signaling deviceincludes an audio alarm that sounds for a predetermined time independentof the length of time a that said at least one switch'is in its secondstate.

apparatus is replaced in the liquid. 7 I v e a:

1. Apparatus for monitoring surface waves on a body of liquid,comprising a piece of flotation material for supporting the apparatus onthe liquid surface, a container supported by said flotation material ina manner to be partially submersed below the liquid surface, saidcoNtainer having an opening in the vacinity of its bottom for liquid topass therethrough into said container and an air opening in the vacinityof its top, thereby allowing liquid to rise within the container to alevel proportional to the height of the liquid surface surrounding saidflotation material, a float pivotably mounted within said container, theangular position of said float being controlled by the level of liquidwithin the container, a first position sensitive electrical switchcarried by said pivotably mounted float in a manner to have oneelectrical state when liquid is below a predetermined level within thecontainer and a second electrical state when liquid is above saidpredetermined level, means electrically connected with said switch forcommunicating its state to a remote location, whereby waves on thesurface of the liquid cause said pivotably mounted float to change itsangular position relative to said container and signals said positionalchange to said remote location, and a second two-state positionsensitive switch carried by said pivotably mounted float and orientedgenerally to be in one of its states when liquid is near saidpredetermined level within said container and in another of its stateswhen the float is not supported against gravity within the container. 2.A swimming pool alarm unit, comprising: a volume of material forfloating on the surface of the swimming pool, said volume of materialformed in the shape of a ring having a circular opening in its center, atubular container positioned within the opening of said ring andthreadedly engaged therewith in a manner that the container may be movedup and down relative to the ring by twisting said container with respectto the ring, said container including a water inlet opening in thevacinity of its bottom and an air opening in the vacinity of its top,thereby allowing water to rise within the container to a levelporportional to the water surface level surrounding said ring offlotation material, at least one position sensitive electrical switchwithin said container positioned to detect the water level within saidcontainer, and means electrically connected with said switch forcommunicating its state to a remote location.
 3. Apparatus formonitoring surface waves on a body of liquid, comprising: a piece offlotation material for supporting the apparatus on the liquid surface, afloat pivotably mounted with respect to said flotation material in amanner to be supported against gravity by the liquid surface, said floatincluding a block of plastic material with a pivot rod extending throughone end thereof for supporting the float with respect to said flotationmaterial in a manner to be rotatable with respect thereto, at least oneposition sensitive electrical switch embedded in said pivotably mountedfloat in a manner to have one electrical state when the liquid surfaceis calm and a second electrical state when a liquid surface wave ofsufficient magnitude strikes the flotation material, and meanselectrically connected with said at least one switch for communicatingits state to a remote location, whereby waves on the surface of theliquid cause said pivotably mounted float to change its angular positionrelative to said container and signals said positional change to saidremote location.
 4. An alarm system according to claim 3 wherein thesingle frequency of the transmitter audio oscillator is outside of thenormal voice frequency range range.
 5. An alarm system according toclaim 3 wherein said means for sounding an audio alarm includes a switchmeans operable in response to a momentary signal output from said filterto connect an audio sounding device and a delay tube to a power sourcefor a predetermined period, said delay tube being connected in a mannerto disconnect said power source from the audio sounding device and thedelay tube after a period of time determined by the characteristics ofthe dElay tube.
 6. Apparatus according to claim 4 wherein said radiofrequency transmitter includes a single-frequency audio oscillatorconnected to modulate said transmitter signal, and further wherein saidreceiver includes a filter circuit tuned to the single frequency of theaudio oscillator to enable said indication means when the receivedsignal includes the modulating single frequency.
 7. Apparatus accordingto claim 3 wherein said means for communicating the state of said atleast one switch to remote location includes: a radio frequencytransmitter carried by said flotation material and connected with saidat least one position sensitive switch in order to transmit a signalwhen said at least one switch is in its said second state, and a radiofrequency receiver located in a position remote from said flotationdevice and tuned to receive said radio frequency signal, said receiverincludes means for giving an indication upon receipt of said signal. 8.Apparatus according to claim 4 wherein said indication means contains analarm means for sounding an audio alarm for a predetermined time afterfirst receiving the radio frequency signal, whereby a mere pulse ofradio frequency energy will sound an alarm of said receiver for saidpredetermined time.
 9. Apparatus according to claim 6 wherein said meansfor communicating the state of said at least one switch to a remotelocation includes: a length of wire electrically connected with saidswitch and extending from said flotation material to said remotelocation, and a signaling device located at said remote location andconnected with said switch by said length of wire, said signaling devicebeing operated when said at least one switch is in its second state. 10.Apparatus according to claim 9 wherein said signaling device includes anaudio alarm that sounds for a predetermined time independent of thelength of time that said at least one switch is in its second state. 11.Apparatus according to claim 6 wherein said float is shaped andsupported in a manner to have its center of gravity displaced a distanceaway from a vertical projection of said pivot rod when the apparatus isremoved from the liquid, thereby to prevent the float from being lockedin a non-operating position when the apparatus is replaced in theliquid.